The disclosure relates to a polycrystalline silicon column and a polycrystalline silicon wafer.
A solar cell is a photoelectric device which generates electric energy by absorbing sunlight and performing photovoltaic conversion by means of a photovoltaic effect. Currently, solar cell materials are mainly silicon materials, as silicon is the second most accessible element on earth and has advantages of having low material cost, is nontoxic, has a high stability and the like, and the application of silicon in the semiconductor field has had a profound foundation.
Solar cells mainly made from silicon material are divided into three types, i.e., monocrystalline silicon, polycrystalline silicon and amorphous silicon. Using polycrystalline silicon as the raw material of a solar cell is mainly based on the consideration of cost. As compared with monocrystalline silicon manufactured by the existing Czochralski method (CZ method) and floating zone method (FZ, method), the cost of the polycrystalline silicon is much cheaper relatively.
The polycrystalline silicon used for manufacturing solar cells is conventionally produced by using a general casting process. In brief, the silicon with a high purity is melted in a mold (e.g., a quartz crucible), and then is cooled under controlled solidification to form a polycrystalline silicon ingot. Then, the polycrystalline silicon ingot is generally cut into square wafers, which will be assembled into a cell by a solar cell manufacturer.
The Journal of Crystal Growth, 312, 2010, p. 1572-1576 published a method for growing high-purity polycrystalline silicon of solar cell by using a directional solidification crystal-growing furnace. As disclosed in the conventional method as described above, and generally conventionally understood, in the crystal-growing process volatile carbon monoxide gas can be easily generated and, if the content of the carbon monoxide incorporated into a silicon melt is too high, the carbon and oxygen will segregate and separately precipitate or otherwise be incorporated into the solidified crystal formed from the melt. The oxygen-containing sites of a solidified ingot are known to behave as gettering sites for impurities and the influence the mechanical strength of a wafer formed therefrom, which can increase the effect of other crystal defects on degrading the crystal quality. Furthermore, the carbon incorporated in the conventional method as described above can easily generate a silicon carbide precipitate through the reaction between the carbon and silicon in the melt, which may reduce the shunt resistance (R shunt) of a cell, thereby causing more electric leakage phenomenon. Therefore, it is believed by those of ordinary skills in the art that, the too-high carbon and oxygen content causes the aforementioned instance, and thus the photovoltaic conversion efficiency is degraded.
The aforementioned description is only used for providing the background technology, rather than admitting that the aforementioned description discloses the subject matter of the disclosure. The aforementioned description does not constitute the prior art of the disclosure, and any of the aforementioned description should not be considered as any part of the disclosure.